Support '#page=<pagenum>' fragment to open at page <pagenum>

Support the '#page=<pagenum>' fragment to specify which page
to open the document at, in addition to the existing '#<pagenum>'
syntax.

For PDF, the '#page=<pagenum>' fragment is specified in RFC 8118,
section 3.

BUG: 406831

autotests/parttest.cpp

@@ -95,6 +95,7 @@ private slots:
     void testAdditionalActionTriggers();
     void testTypewriterAnnotTool();
     void testJumpToPage();
+    void testOpenAtPage();
     void testForwardBackwardNavigation();
     void testTabletProximityBehavior();
     void testOpenPrintPreview();
@@ -1794,6 +1795,26 @@ void PartTest::testJumpToPage()
     QCOMPARE(part.m_pageView->verticalScrollBar()->value(), pageWithSpaceTop - 4);
 }
 
+void PartTest::testOpenAtPage()
+{
+    const QString testFile = QStringLiteral(KDESRCDIR "data/simple-multipage.pdf");
+    QUrl url = QUrl::fromLocalFile(testFile);
+    Okular::Part part(nullptr, nullptr, QVariantList());
+
+    const uint targetPageNumA = 25;
+    const uint expectedPageA = targetPageNumA - 1;
+    url.setFragment(QString::number(targetPageNumA));
+    part.openUrl(url);
+    QCOMPARE(part.m_document->currentPage(), expectedPageA);
+
+    // 'page=<pagenum>' param as specified in RFC 3778
+    const uint targetPageNumB = 15;
+    const uint expectedPageB = targetPageNumB - 1;
+    url.setFragment("page=" + QString::number(targetPageNumB));
+    part.openUrl(url);
+    QCOMPARE(part.m_document->currentPage(), expectedPageB);
+}
+
 void PartTest::testForwardBackwardNavigation()
 {
     const QString testFile = QStringLiteral(KDESRCDIR "data/simple-multipage.pdf");

part.cpp

@@ -1670,7 +1670,17 @@ bool Part::openUrl(const QUrl &_url, bool swapInsteadOfOpening)
     if (url.hasFragment()) {
         const QString dest = url.fragment(QUrl::FullyDecoded);
         bool ok = true;
-        const int page = dest.toInt(&ok);
+        int page = dest.toInt(&ok);
+
+        if (!ok) {
+            const QStringList parameters = dest.split(QChar('&'));
+            for (const QString &parameter : parameters) {
+                if (parameter.startsWith(QStringLiteral("page="), Qt::CaseInsensitive)) {
+                    page = dest.midRef(5).toInt(&ok);
+                }
+            }
+        }
+
         if (ok) {
             Okular::DocumentViewport vp(page - 1);
             vp.rePos.enabled = true;